Satellite communications systems transmit content over large geographic regions. In a typical satellite communications system, end users interface with the system through user terminals. The user terminals communicate, via one or more satellites, with one or more gateway terminals. The gateway terminals may process and route data to and from one or more networks according to various protocols.
A typical hub-spoke spot beam satellite communications system may include a non-processing “bent pipe” spot beam satellite, many user terminals, and a smaller number of gateway terminals. Each user terminal may be connected to a network, such as the internet, via a series of communication links.
A forward link of a satellite communications system may consist of a forward uplink transmission from a gateway terminal to a satellite, a “bent pipe” repeater at the satellite, and a forward downlink transmission to a group of user terminals located in a common spot beam. The forward link may carry data from a gateway terminal to many different user terminals. The forward link may utilize, for example, time Division Multiplexing (TDM) and/or Frequency Division Multiplexing (FDM) of data into RF transmissions.
A return link of a satellite communications system may consist of a return uplink transmission from user terminals in a common spot beam to a satellite, and a return downlink transmission from the satellite to a gateway terminal servicing the spot beam. Transmissions from many user terminals may utilize the return link using Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), or the like.
For typical multiple access schemes (e.g., TDMA, FDMA, CDMA, etc.), bandwidth utilization varies with time. As a result, interference to and from other spot beams (both co-polarized and cross-polarized) or even within the same beam may be time varying and dynamic. User terminals generally transmit only when they have data that needs to be transmitted and when they have been assigned one or more slots, frequencies, CDMA codes, or the like for transmission.
In moderate frequency re-use environments that are typical of high capacity spot beam satellites, interference from nearby spot beams operating on the same frequency can cause fluctuation of an end-to-end signal to noise plus interference ratio (SINR). The end-to-end SINR may vary by as much as 5 dB or more. Furthermore, interference can be very dynamic. Bursts in a TDMA system may be as short as 10 μSec or less in duration. Traditional closed loop power control schemes that adjust effective isotropic radiated power (EIRP) at user terminals in response to a measured SINR cannot track dynamic interference because round trip delay through a geo-synchronous satellite is typically more than 500 mSec (including processing time at the gateway terminals). As a result, such approaches perform poorly in dynamic and high interference environments.
Thus, there is a need for improved satellite link power control in dynamic and high interference environments.